A route information processing system, that is, a navigation system that is installed in a vehicle, serves as a route guide that guides the driver of the vehicle from the present location to a destination. The route guide estimates and presents the time required to arrive at the destination using a travel speed estimated from the past travel speed on each road included in the route guide.
The travel speed on each road differs between a weekday and a holiday and depending on the time of day. It is thus difficult to estimate the subsequent travel speed from the past travel speed that changes depending on the time and day. Patent document 1 discloses one example of a technique for estimating the subsequent travel speed from the past travel speed.
The technique described in patent document 1 includes factual information of travel speeds for roads extracted from a network of roads in association with time and day. Factual information related to a first period until the present time and factual information related to a second period that does not include the present time are acquired to calculate a similarity degree of the acquired factual information related to the first period and the acquired factual information related to the second period. Then, based on the calculated similarity degree, a travel speed that is related to a third period, which follows the second period, is determined as an estimated value of the travel speed after the present time.